1. Field of the Invention
The present invention relates generally to optical fiber amplifiers, and more particularly to a fiber amplifier having a core doped with transition metal.
2. Description of the Related Art
Many types of optical fiber amplifiers are known in the art and are suitable for various optical communication bands.
U.S. Pat. No. 6,646,796 disclosed a wide band erbium-doped fiber amplifier. It connected two erbium-doped fiber amplifiers to achieve a super wide band amplifier. The first erbium-doped fiber amplifier pumped by a 980 nm laser diode was used to amplify the input optical signal of the C-band, which has a wavelength ranging from 1530 nm to 1560 nm. The second erbium-doped fiber amplifier pumped by a 1480 nm laser diode was used to amplify the input optical signal of the L-band, which has a wavelength ranging from 1570 nm to 1600 nm.
The disadvantage of the above-mentioned U.S. patent is that the band of the optical signal that can be amplified falls only in the C-band and the L-band, which has a bandwidth shorter than 80 nm. This bandwidth is only a part of a 300 nm bandwidth used in the optical communication. Besides, it needs two erbium-doped fiber amplifiers and two pumping lasers of different wavelength, which increase the cost of the system.
U.S. Pat. No. 6,515,795 disclosed a thulium-doped fiber amplifier. The fiber has a borosilicate glass material cladding and a core comprising a germinate glass material doped with Tm3+. It can amplify the optical signal of 1400-1540 nm with a pumping source. The pumping source used in the amplifier is a semiconductor laser, having essentially a wavelength of 780-800 nm.
The disadvantage of the above-mentioned amplifier is that the melting point of the fiber with borosilicate glass material cladding is about 800° C. such that the fiber cannot be connected by fusion to the present fused silica fiber that has a melting point of 1600° C. It increases the system cost by using additional optical elements or mechanical structures as optical couplers. In addition, the bandwidth of the optical signal that can be amplified is about 160 nm, which does not cover the whole 300 nm bandwidth of the optical communication.
U.S. Pat. No. 5,805,332 disclosed a praseodymium-doped fiber amplifier. The fiber has a fused silica cladding and a core comprising zirconium dioxide doped with praseodymium ion. The fiber amplifier is well suited for use in the 1300 nm band when pumped with an optical source having a wavelength of about 1000 nm. However, the 1300 nm band does not cover the whole band in the optical communication.